Improved method for preparing cell stack by uniform thermal activation of adhesives

Abstract

The invention relates to a method for producing a cell stack, in particular a cell stack for electrochemical storage, in which at least an anode electrode, a separator layer and a cathode electrode are repeatedly stacked or folded or wound on each other, wherein at least one layer is coated on one side or both sides with a thermally activatable adhesive or at least one layer is provided with an adhesive, an electrically conductive layer, in particular an anode electrode and / or a cathode electrode, is electromagnetically and / or electrically heated, the adhesive is thermally activated as a result of the heating of the electrically conductive layer, and in particular, the adhesive is thermally activated as a result of the heating of the electrically conductive layer. The anode electrode, the isolation layer, and the cathode electrode are connected to each other to form a cell stack. The invention also relates to a device for producing a cell stack and to an electrochemical storage device having at least one cell stack.

Description

[0001] The present invention relates to a method for producing a cell stack, in particular a method for producing a cell stack for an electrochemical storage device, in which at least an anode electrode, a separator layer, and a cathode electrode are repeatedly stacked, folded, or wound one upon another. The present invention also relates to a device for producing a cell stack and an electrochemical storage device having at least one cell stack.

[0002] In the production of electrochemical storage devices such as lithium-ion batteries, several alternating layers of anode, cathode, and separator are typically arranged in a battery stack. These layers are coated with a heat-activatable adhesive and then bonded together using heat and force. To this end, the layers are positioned between two heating plates that act on the layers.

[0003] However, heating the stack layers via heating plates results in a non-uniform temperature distribution along the stack's height or thickness. This non-uniform temperature distribution prevents uniform bonding between the stack layers and across all stack layers using heat-activated adhesives. Furthermore, complete heating of all stack layers is delayed by the electrical and thermal insulation properties of the isolation layer, limiting the system's output during stack preparation.

[0004] Known approaches are to press the layers of the battery stack together with greater force during heating or to apply higher temperatures to the layers to accelerate the bonding process. However, these measures can adversely affect the material properties of the battery components or individual layers of the battery stack.

[0005] The object of the present invention is therefore to provide a method for producing a cell stack, in particular for an electrochemical storage device, which allows for rapid and uniform bonding of the layers of the cell stack. This object is achieved by the features specified in claim 1. Further advantageous embodiments of the invention are part of the dependent claims.

[0006] According to one aspect of the present invention, a method for preparing a battery stack is provided. In particular, a battery stack for an electrochemical storage device, such as a lithium-ion battery, is provided. This battery stack includes a plurality of anode electrodes, separators, and cathode electrodes, which are repeatedly stacked, folded, or wound one upon another. Furthermore, other layers, such as those containing graphite or other materials, may also be provided.

[0007] The anode electrode may, for example, consist of a copper foil or a copper carrier foil coated on one or both sides with an anode substrate. Similarly, the cathode electrode may, for example, consist of an aluminum foil or an aluminum carrier foil coated on one or both sides with a cathode substrate.

[0008] For the sake of simplicity, possible additional layers commonly found in the lithium-ion battery field will not be further described. To form a monolithic or integrated battery stack, adhesive layers are used or certain layers are pre-coated with adhesive. For example, a separator layer may be coated with a heat-activated adhesive on one or both sides, or may be provided with adhesive.

[0009] After the anode electrodes, separator layers and cathode electrodes have been arranged, the conductive layers, in particular the copper and aluminum foils of the anode electrodes and / or cathode electrodes and / or the additional layers or grids, are electromagnetically and / or electrically heated. In contrast to the prior art, in which a heat source is pressed onto the battery stack from the outside and the heat slowly diffuses from the outside to the inside, heat is now generated directly in all the conductive layers of the battery stack. This measure can eliminate time-consuming and uneven heat conduction. By heating the anode electrodes and / or cathode electrodes, the adhesives of the individual separator layers are directly or immediately thermally activated. By thermally activating the adhesive, the anode electrodes, separator layers and cathode electrodes are bonded together to form an integrated battery stack. This completes the exemplary battery stack.

[0010] Depending on the design and requirements of the method, additional processing steps, such as electrical connection of contact strips, final dimensioning, application of coatings or packaging, arrangement of positioning aids, etc., may be followed or performed as part of the method.

[0011] According to another aspect of the present invention, a device for preparing a battery stack is provided. The device is suitable for carrying out the method according to the present invention. For this purpose, the device can have a receiving space for receiving at least one bundle of layers, which are bonded together to form the layers of the battery stack. In addition, at least one heat source is provided, which can generate heat in the conductive layers of the bundle by electromagnetic or electrical induction. Depending on the design of the device, a pressure device having a lower mold and an upper mold can be used to apply pressure to the layers. A control unit can be used to control and regulate the generation of heat and the pressure provided by the pressure device, for example based on measurement data from sensors.

[0012] According to another aspect of the present invention, an electrochemical storage device is provided. The electrochemical storage device has at least one battery housing and can be designed, for example, as a battery cell based on lithium-ion technology. At least one battery stack produced according to the method of the present invention is arranged in the battery housing. The battery stack produced by the method of the present invention is not limited to lithium-ion technology and can therefore be used for a wide variety of electrochemical cells that require an integrated battery stack having multiple layers.

[0013] By releasing heat internally to thermally activate the adhesive, the heating time required for the adhesive to develop its bonding properties can be reduced. Furthermore, by introducing heat into the conductive layer, a more uniform temperature distribution can be achieved both laterally and within the layer, as well as across the thickness of the battery stack. Due to the uniform temperature profile throughout the battery stack, the outer layers are not subject to thermal stress, or are subject to less stress than the inner layers. This prevents harmful changes in the material properties of the battery stack layers.

[0014] Heat-activatable adhesives can be designed as hot melt adhesives, for example based on polyurethane, which solidify below a temperature threshold and become tacky or sticky above the temperature threshold. Alternatively, two-component adhesives with a heat-activatable curing agent can be used as heat-activatable adhesives. The curing agent liquefies as the temperature rises and can then react with the resin. For example, a heat-activatable adhesive can be designed as PVDF (polyvinylidene fluoride).

[0015] The conductive layers of a battery stack can be heated particularly effectively if at least one magnetic coil is positioned adjacent to the anode and / or cathode electrodes. The magnetic coils are controlled to generate a time-varying magnetic field, which inductively heats the anode and / or cathode electrodes. In particular, components of the anode and / or cathode electrodes with high electrical conductivity are heated. Examples of such components include copper and aluminum foil.

[0016] Depending on the size of the battery stack, it may be advantageous to use several magnetic coils to generate uniform eddy current induction in the conductive layers. The anode and / or cathode electrodes typically have aluminum and copper carrier foils embedded in or bonded to the respective anode and cathode substrates. Due to their high electrical conductivity, the aluminum and copper carrier foils can be heated inductively particularly quickly and efficiently.

[0017] Advantageously, the magnetic field generated by the coil can be oriented perpendicular to the plane of the layers or parallel to the surface normal. Thus, according to Maxwell's third equation, eddy currents can be induced in the conductive layers due to the time-varying magnetic field. However, induced eddy currents exhibit power losses, which have the effect of heating each individual foil of the anode and cathode electrodes. Depending on the amplitude of the magnetic field over time, eddy currents are preferably induced in all conductive layers of the cell stack.

[0018] According to another embodiment example, the anode electrode and / or cathode electrode, in particular a copper foil and an aluminum foil, are electrically contacted at at least two contact points by at least one current source and subjected to a constant or varying current in order to heat the anode electrode and / or cathode electrode by Joule heating. By this alternative or additional measure, the conductive layer can be heated by directly applying current and the resulting power loss in order to thermally activate the adhesive.

[0019] According to another embodiment, the anode electrode, cathode electrode, and separator are positioned within a pressurizing device. Advantageously, while the separator adhesive is being heat-activated, or after the separator adhesive has been heat-activated, the anode electrode, cathode electrode, and separator are pressed together by the pressurizing device using a constant or time-varying force. Applying pressure from the pressurizing device ensures the ultimate bonding result. Varying the pressure over time allows for particularly precise control of the adhesive's bonding properties.

[0020] The cell stack can be heated particularly uniformly if the anode and / or cathode electrodes are inductively heated by at least two magnetic coils integrated into the upper and / or lower molds of the pressing device. This heating occurs, for example, by inducing eddy currents in the copper and aluminum foils of the respective electrodes.

[0021] According to another embodiment example, the device includes a guide device for guiding the magnetic field generated by the magnetic coil at least in certain areas, wherein the magnetic field generated by the magnetic coil is guided via an upper portion of the guide device located in the upper mold, via a lower portion of the guide device located in the lower mold, and via both sides of the guide device. The guide device or a corresponding portion of the guide device can, for example, form the exterior of the coil core or magnetic core and is used to guide the external magnetic field lines. The magnetic field lines directly generated by the magnetic coil can flow through the layers of the battery stack and be deflected or directed to the exterior of the battery stack by portions of the guide device.

[0022] The guide device sections can be electrically conductively contacted or spaced apart. Furthermore, the guide device sections can be made of a ferromagnetic metal alloy. To reduce eddy current losses in the guide device, the guide device sections can be packaged in sheet metal. This measure allows for controlled magnetic return and particularly energy-efficient operation of the magnetic coil.

[0023] Depending on the design, parts of the guide device can be cooled by air or liquid. Similarly, at least one magnetic coil can be air-cooled or liquid-cooled.

[0024] The device for preparing a battery stack can be designed to be particularly flexible if the magnetic field generated by the at least one magnetic coil is guided through two side sections of a guide device, which are arranged in the pressurizing direction between the upper and lower sections of the guide device, or arranged laterally to the upper and lower sections of the guide device. This arrangement of the guide device sections enables flexible insertion of the battery stack into the receiving space. For example, the upper mold with its upper or side sections can be removed to arrange a bundle of layers in the receiving space to prepare the battery stack, and the battery stack can be removed from the receiving space after the joining process.

[0025] According to another embodiment, during the thermal activation of the adhesive along at least one anode layer and / or cathode layer, the temperature is measured by a temperature measuring device. The use of the temperature measuring device and its corresponding connection to a control unit enable precise control of the heating in the conductive layers of the cell stack. Consequently, the at least one magnetic coil can be controlled and monitored based on the measurement data determined by the temperature measuring device.

[0026] The temperature measuring device can be implemented in a particularly versatile manner if the temperature is measured directly by at least one thermoelement and / or measuring resistor of the temperature measuring device. In an alternative embodiment, the temperature is measured indirectly by the temperature measuring device measuring the electrical conductivity of at least one anode layer and / or cathode layer. This allows for particularly precise temperature determination across the entire width or length of the layer.

[0027] Several embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. They show:

[0028] Figure 1 is a schematic cross-sectional view of an apparatus for preparing a battery stack to illustrate a method according to one embodiment of the present invention,

[0029] Figure 2 is a schematic cross-sectional view of an apparatus for preparing a battery stack according to a second embodiment,

[0030] Figure 3 is a schematic cross-sectional view of an apparatus for preparing a battery stack according to a third embodiment,

[0031] Figure 4 is a schematic cross-sectional view of an electrochemical storage device having a battery stack, and

[0032] Figure 5 yes Figure 4 Schematic detail view of a cross-section shown to illustrate the composition of the battery stack.

[0033] In the drawings, like reference numerals denote like elements or structural components. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale, and some of these elements are exaggerated and positioned for clarity. In addition, the particular shapes of the elements drawn are not intended to convey any information about the actual shape of the respective elements, but are selected solely for ease of identification in the drawings.

[0034] Figure 1 A schematic cross-sectional view of an apparatus 10 for preparing a battery stack 100 is shown to illustrate a method according to an embodiment of the present invention. The apparatus 10 according to a first embodiment is shown.

[0035] The battery stack 100 produced by the method is particularly useful for an electrochemical storage device 200, such as Figure 4 In the embodiment shown, the battery stack 100 includes a plurality of anode electrodes 101, separators 103, and cathode electrodes 102, which are repeatedly stacked, folded, or wound on top of each other.

[0036] To form a monolithic or integrated battery stack 100, an adhesive layer (not shown) is applied, or certain layers are pre-applied with adhesive. For example, one or both sides of the isolation layer 103 may be coated with or moistened with a heat-activatable adhesive. Depending on the configuration of the method, any layer 101, 102, or 103 may be provided with a heat-activatable adhesive. The use of an adhesive in conjunction with the isolation layer 103 is used herein to illustrate the method.

[0037] In a first step of the method, the layers 101, 102, 103 of the battery stack 100 are placed in the receiving space 11 of the device 10. The respective layers 101, 102, 103 are aligned relative to each other and can be temporarily prevented from unintentional sliding by means of clamps, supports or by the receiving space 11. As an example, in Figure 4 Detailed illustrations of the individual layers 101 , 102 , and 103 of the battery stack 100 are shown.

[0038] The receiving space 11 of the device is designed to receive at least one bundle of layers 101, 102, 103, which are bonded together to form a cell stack 100. Furthermore, at least one heat source 20, 21 is provided, which can generate heat in the electrically conductive layers 101, 102 of the bundle electromagnetically 20 and / or electrically 21. Thus, after the layers 101, 102, 103 have been provided, the electrically conductive layers 101, 102, which in the illustrated embodiment are designed as anode electrodes 101 and / or cathode electrodes 102, are heated electromagnetically and / or electrically in the further steps of the method.

[0039] In the illustrated embodiment, apparatus 10 includes a pressurizing device 30 with a lower mold 31 and an upper mold 32 for applying a pressure F to layers 101, 102, and 103. A control unit 40 is used to control and regulate the heat generated by heat sources 20 and 21 and the pressure provided by pressurizing device 30, for example, based on measurement data from sensors. A temperature measuring device 41 is schematically shown for directly or indirectly determining the temperature of layers 101, 102, and 103. Temperature measuring device 41 can use thermal and / or electrical sensors to measure the temperature of layers 101, 102, and 103. The thermal sensors can determine the temperature based on direct contact with layers 101, 102, and 103, or based on contactless measurement, such as by recording infrared light.

[0040] In order to generate uniform heating in the conductive layers 101 and 102, the control unit 40 can control the two magnetic coils 20 to generate a time-varying magnetic field B, which inductively heats the anode electrode 101 and / or the cathode electrode 102. The magnetic lines of force of the generated magnetic field B are given by Figure 1 、 Figure 2 and Figure 3 Indicated by the arrow in .

[0041] Alternatively or additionally, the anode electrode 101 and / or the cathode electrode 102 can be electrically contacted at at least two contact locations by at least one current source 21 and subjected to a constant or varying current to cause heating of the anode electrode 101 and / or the cathode electrode 102 by Joule heating. The current source 21 can also be controlled by the control unit 40.

[0042] By heating the anode electrode 101 and / or cathode electrode 102, the adhesive of each separator layer 103 is directly or immediately thermally activated. Due to the thermal activation of the adhesive, the anode electrode 101, separator layer 103, and cathode electrode 102 are bonded together to form an integrated battery stack 100. This step can complete the battery stack 100. Depending on the design and requirements of the method, additional processing steps, such as electrical connection of contact sheets, final dimensional adjustment, application of coatings or packaging, and placement of positioning aids, may be followed or implemented as part of the method.

[0043] Figure 2 1 shows a schematic cross-sectional view of an apparatus 10 for preparing a battery stack 100 according to a second embodiment. Figure 1 In contrast to the embodiment example shown, here a device 10 is shown which has a guide device 50 for guiding, at least in certain areas, the magnetic field B generated by the magnetic coil 20. For this purpose, the guide device 50 has an upper part 51, a lower part 52 and two side parts 53.

[0044] The upper part 51 is integrated into the upper mold 31 of the press device 30. The lower part 52 is integrated into the lower mold 32 of the press device 30. The side parts 53 of the guide device 50 are located laterally to the upper part 51 and the lower part 52 and form a substantially closed circuit for the magnetic return. In the embodiment example shown, the receiving space 11 is located in the center of this circuit.

[0045] In the embodiment example shown, the side portion 53 is located between the upper portion 51 and the lower portion 52 along a thickness or height direction H. The height direction H corresponds to the contact pressure direction in the embodiment example shown.

[0046] Figure 3 1 shows a schematic cross-sectional view of an apparatus 10 for preparing a battery stack 100 according to a third embodiment. Figure 2In contrast to the device 10 shown, the side portions 53 of the guide device 50 are laterally offset relative to the upper portion 51 and the lower portion 52 in the transverse direction L. As a result, the upper mold 31 and the lower mold 32 can move freely in the height direction H relative to the side portions 32 .

[0047] For clarity, Figure 2 and Figure 3 The control unit 40 and the temperature measuring device 41 are not shown.

[0048] Figure 4 A schematic cross-sectional view of an electrochemical storage device 200 having an integrated cell stack 100 is shown. Electrochemical storage device 200 has a battery housing 201 and can be designed, for example, as a battery based on lithium-ion technology. At least one integrated cell stack 100 produced according to the method of the present invention is arranged in cell housing 201. Cell stack 100 is electrically contacted, for example, via electrodes 202 and 203 on two opposing sides.

[0049] exist Figure 5 In the Figure 4 A schematic detailed view of a cross-section is shown to illustrate the composition of a battery stack 100. The battery stack 100 has a plurality of anode electrodes 101, separators 103 and cathode electrodes 102, which are repeatedly stacked, folded or wound on top of each other and connected to each other by the method already described.

[0050] In the embodiment example shown, each anode electrode 101 comprises a copper foil 104 or a copper carrier foil, both sides of which are coated with an anode substrate 105 .

[0051] Similarly, each cathode electrode 102 has an aluminum foil 106 or aluminum carrier foil, both sides of which are coated with a cathode substrate 107 .

[0052] The cell stack 100 is terminated on both sides along the height direction H by anode electrodes 101 , wherein the anode electrodes 101 , the separators 103 and the cathode electrodes 102 alternate continuously along the height direction.

Claims

1. A method for producing a battery stack (100), in particular a battery stack (100) for an electrochemical storage device (200), wherein at least an anode electrode (101), a separator (103) and a cathode electrode (102) are repeatedly stacked or folded or rolled on top of each other, wherein at least one layer (101, 102, 103) is coated on one or both sides with a heat-activatable adhesive or at least one layer (101, 102, 103) is provided with an adhesive, wherein the conductive layers (101, 102), in particular the anode electrode (101) and / or the cathode electrode (102), are electromagnetically and / or electrically heated, wherein the adhesive is heat-activated by heating the conductive layers (101, 102), and, in particular, the anode electrode (101), the separator (103) and the cathode electrode (102) are joined together to form an integrated battery stack (100).

2. The method according to claim 1, wherein at least one magnetic coil (20) is arranged adjacent to the anode electrode (101) and / or the cathode electrode (102), wherein the magnetic coil (20) is driven to generate a time-varying magnetic field (B), and the anode electrode (101) and / or the cathode electrode (102) are induced heated by the time-varying magnetic field (B).

3. A method according to claim 1 or 2, wherein the anode electrode (101) and / or the cathode electrode (102) are electrically contacted at at least two contact locations by at least one current source (20) and are subjected to a constant or varying current to cause heating of the anode electrode (101) and / or the cathode electrode (102) by Joule heat.

4. A method according to any one of claims 1 to 3, wherein the anode electrode (101), the cathode electrode (102) and the isolation layer (103) are located in a pressurizing device (30), wherein the anode electrode (101), the cathode electrode (102) and the isolation layer (103) are pressed together by the pressurizing device (30) at a constant pressure or a time-varying pressure (F) when the adhesive is heat-activated or after the adhesive has been heat-activated.

5. The method according to claim 2 and claim 4, wherein the anode electrode (101) and / or the cathode electrode (102) is inductively heated by at least one magnetic coil (20) integrated in the upper mold (31) and / or the lower mold (32) of the pressing device (30).

6. A method according to claim 5, wherein a guide device (50) is provided for guiding the magnetic field (B) generated by the magnetic coil (20) at least in certain areas, wherein the magnetic field (B) generated by the magnetic coil (20) is guided via an upper part (51) of the guide device (50) located on the upper mold (31), via a lower part (52) of the guide device (50) located on the lower mold (32), and via two side parts (53) of the guide device (50).

7. A method according to claim 6, wherein the magnetic field (B) generated by at least one magnetic coil (20) is guided via two side parts (53) of the guide device (50), which are arranged in the pressure direction between the upper part (51) and the lower part (52) of the guide device (50) or laterally next to the upper part (51) and the lower part (52) of the guide device (50).

8. The method according to any one of claims 1 to 7, wherein the temperature is measured by a temperature measuring device (41) during the thermal activation of the adhesive along at least one anode layer (101) and / or cathode layer (102).

9. The method according to claim 1 , wherein the temperature is measured directly by at least one thermal element and / or a measuring resistor of a temperature measuring device ( 41 ); or The temperature is indirectly measured by measuring the electrical conductivity of at least one anode layer (101) and / or cathode layer (102) using a temperature measuring device (41).

10. An apparatus (10) for producing a battery stack (100), wherein the apparatus (10) is adapted to perform the method according to any one of the preceding claims.

11. An electrochemical storage device (200) comprising at least one battery housing (201), wherein at least one battery stack (100) is arranged in the battery housing (201), the battery stack (100) being produced by the method according to any one of claims 1 to 9.

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